Method for stabilizing polydiene polymer reacted with sulfur dioxide and resulting products



Patented Dec. 18, 1951 METHOD FOR STABILIZING POLYDIENE POLYMER REACTEDWITH SULFUR DI- OXIDE AND RESULTING PRODUCTS Johan Michael Goppel,Gottfried Ernst Rumscheidt, and Johannes Thomas Hackmann, Amsterdam,Netherlands, assignors to Shell Development Company, San Francisco,Calif., a corporation of Delaware No Drawing. Application April 26,1949, Serial No. 89,803. In the Netherlands May 18, 1948 15 Claims. 1

This invention is directed to a process for the stabilization ofproducts formed on reacting inorganic acidifyin compounds with rubberypolymers comprising high molecular weight, polyunsaturated compounds.The invention also relates to the resulting stabilized reactionproducts.

The term high molecular weight, polyunsaturated compound, as employedherein, embraces those compounds having a molecular weight of at least5,000 and which contain a plurality of unsaturated linkages in themolecule. These compounds are either polymers of organic compoundscontaining a plurality of unsaturated linkages in the molecule, or arecopolymers of such multiple-unsaturated compounds with other unsaturatedorganic compounds of one type or another. The term includes the variousnatural rubbers such as latex, crepe, sheet, caoutchouc, gutta percha,balata, and cyclo rubbers, as well as unsaturated synthetic rubbers.Representative synthetic polymers of high molecular weight are thepolymerization products of butadiene and those of its homologues andderivatives, as, for example, methyl butadiene polymers, dimethylbutadiene polymers, pentadiene polymers, and chloroprene polymers(neoprene synthetic rubber). Representative copolymers of high molecularweight which come within the term are those formed from butadiene, itshomologues and derivatives, with other unsaturated organic compounds.Among the latter are the acetylenes, as vinyl acetylene, the olefins, asisobutylene which copolymerizes with butadiene to form butyl syntheticrub-her; the vinyls, as vinyl chloride, acrylic acid, acrylonitrile(which polymerizes with butadiene to form the synthetic rubber Buna N),methacrylic acid, and styrene, the latter compound polymerizing withbutadiene to form the synthetic rubber Buna S; as well as the vinylesters and various unsaturated aldehydes, ketones and ethers, e. g.,acrolein, methyl isopropenyl ketone, and vinyl ethyl ether. Theabove-defined, polyunsaturated, high molecular weight compounds,including both natural and synthetic rubbers, may properly be termedhigh molecular weight polymers of diene-hydrocarbons, or preferably,rubbery polymers of at'least one compound selected from the groupconsistin of the conjugated diolefines and chloroprene.

As employed herein, the term inorganic acidifying compound embraces thevarious inorganic acids and acid anhydrides wherein the acid-formingelement (as sulfur, nitrogen or phosphorus, for example), if possessingseveral valencies, is present, in a valency other than the highestthereof. Preferred acidifying compounds are the acid anhydrides, sulfurdioxide, phosphorus trioxide and nitrous trioxide, as well as the acidsformed from these anhydrides. Other useful acidifying compounds arehydrogen sulfide, hydrochloric acid, hydrobromic acid, hydroiodic acid,and hyrofluoric acid. The term does not include such compounds as sulfurtrioxide, phosphorus pentoxide, nitrogen pentoxide, or theircorresponding acids, for in all these compounds the acid-formingelement, which is here either sulfur, phosphorus or nitrogen, is presentin the highest of several possible valencies. Of the various acidifyingcompounds set forth herein, the most preferred compound for employmentin the 7 present invention is sulfur dioxide.

It is known that the high molecular weight polyunsaturated compoundslend themselves well to the production of various shapes, includingthose of a continuous, non-supported nature, as filaments, rods, strips,sheets, and the like. Furthermore, it is known that the properties ofsuch shapes may be improved by reacting the unsaturated, high molecularweight compound with one or more of the inorganic acidifying compoundsmentioned above, particularly sulfur dioxide. The exact nature of thisreaction is not clearly understood, though it is evident that a quantityof the acidifying ingredient is taken up in one form or another by thehigh molecular Weight reactant. The extent of this reaction is normallymeasured by, and expressed in terms of, the amount of acid-formingelement (sulfur,

, phosphorus or nitrogen, for example) present in the resulting reactionproduct.

It has also been possible to improve the nature of the foregoingreaction products by incorporating therein, normally prior to thereaction with sulfur dioxide or other acidifying ingredient, a quantityof a low molecular weight, unsaturated compound. The resulting reactionproduct has a numb-er of advantages, chief among which is a greatlyimproved acceptance for all the commonly employed dyestuffs.Representative unsaturated compounds which may be employed in thismanner, all of which have a molecular weight of below 5,000 arealkadienes such as butadiene and 1,5- hexadiene, and aikenyl compoundssuch as allyl alcohol, allyl chloride, allyl acetate, allyl capronate,allyl isothiocyanate, allyl oleate, and more especially, diallylcompounds such as diallyl phthalate and diallyl adipate. The method bywhich unsaturated reactants of both high and low molecular weight areutilized in forming reaction products with acidifying compounds formsthe subject of copending application, Serial No. 15,048, filed March 15,1948, and reference is hereby made to said application for a morecomplete description of the invention there disclosed.

It should be noted that while the high molecular weight, polyunsaturatedcompounds, or mixtures of both high as well as low molecular weightunsaturated compounds, may be reacted with the acidifying compoundwithout prior modification of either reactant, improved results areobtained when the unsaturated compounds are first activated by treatmentwith a hydroperoxide such as decalin hydroperoxide, or tetralinhydroperoxide. Activation methods of this nature are disclosed incopending applications, Serial Nos. 760,924, filed July 14, 1947, nowPatent No. 2,469,847, and 788,312, filed November 26, 1947, now PatentNo. 2,558,498, to which applications reference is here made. Theperoxide treatment is also disclosed in copending application Serial No.15,048, referred to above, as said activation treatment relates tomixtures of high and low molecular weight unsaturated reactants.

While the reaction products discussed above have proven well adapted formany uses, they have proven particularly useful when formed intofilaments of the type which can be Woven into textiles, either alone orin conjunction with fibers of other materials. Thus, filaments producedby spinnin a peroxide-activated rubber solution into a sulfurdioxide-containing coagulating bath have a high elementary denier, withgood tensile strength, a relatively high degree of elongation prior torupture, and good flexibility and other characteristics making for easeof WOIkil'lg and handling. In view of these many favorable qualities, ithas been highly disappointing to realize that even in the case of thebest reaction products hitherto obtainable, deterioration of thefilament or other shape with age,heating and/or exposure to ultra-violetlight is unduly rapid. This deterioration is manifested in a variety ofways, but chiefly in a sharp falling off in tensile strength and in thedegree of permissible stretch prior to rupture. In many instancesundesirable color changes also ensue. These various changes are greatlyspeeded up as the objects under consideration are heated, particularlyabove 100 C., or are exposed to ultra-violet or other light rays. It hasbeenobserved that the deterioration in physical properties is attendedby a loss of sulfur dioxide or equivalent acid constituent from thereaction product, a loss which is generally proportional to theaforementioned deterioration. Accordingly, the rapidity with which agiven product loses its acid constituent may also be taken as a measureof its stability, i. e., its resistance to deterioration with age,heating and/or exposure to light.

It is an object of the present invention to provide a method forobtaining stable products of the type formed on the reaction of highmolecular weight, polyunsaturated compounds with inorganic acidifyingcompounds. A more particular object is to provide reaction products ofthis character which are stable and resist deterioration on being aged,heated, or exposed to light. A still further object is to providefilaments and like continuous, non-supported shapes composed of suchreaction products which are characterized by a continued high tensilestrength and high degree of stretch prior to rupture, as well as by arelatively small loss of acidifying compound, when aged, heated orexposed to light. The nature of still other objects will be apparentfrom the nature of the following description.

It has been discovered that improved resistance to deterioration withage, heating and/or exposure to light rays may be imparted to objectscomposed of the products formed on reacting high molecular weight,polyunsaturated .com-

pounds with inorganic acidifying compounds, by incorporating in saidobjects one or more stabilizer compounds selected from the groupconsisting of the salts and esters of cyanic, isocyanic, thiocyanic andisothiocyanic acids. The improvement is particularly marked as regardsimproved stability at high temperatures.

As representative compounds coming within this group there may bementioned sodium cyanate, potassium cyanate, ammonium cyanate, ethylisocyanate, phenyl isocyanate, iscpropyl isocyanate, isobutylisocyanate, allyl isocyanate, lead cyanate, mercurous cyanate, potassiumisocyanate, sodium isocyanate, ammonium isocyanate, potassiumthiocyanate (potassium rhodamide) ammonium thiocyanate (ammoniumrhodamide), allyl thiocyanate, ethylene thiocyanate, methylenethiocyanate, thiocyanoacetone, phenyl thiocyanate, benzyl thiocyanate,sodium isothiocyanate, and potassium isothiocyanate. A preferred groupof compounds for use in the present invention is that made up of thealkali metal and ammonium salts of thiocyanic acid.

The foregoing salt and ester compounds may be employed either alone, incombination with one another, or with other types of stabilizercompounds. Among the latter may be mentioned various urea-type compoundssuch as urea, thiourea, guanidine, N,N'-diphenyl urea, and N,N'-diphenyl thiourea, compounds of this type being described in copendingapplication Serial No. 37,056, filed July 3, 1948; amines and aminesalts, representative compounds of the latter type, as described incopending application Serial No. 89,801, filed April 26, 1949, beinghexamethylenetetramine, melamine, heptadecylamine, benzyl amine, and thelike; and amides such as dicyandiamide, acetamide, zincdimethyldithiocarbomate, and thiuram disulfide, the use of amidestabilizers being described in copending application Serial No. 89,802,filed April 26, 1949.

The stabilizer chosen, which, as noted above, may be one or a mixture ofseveral compounds, can be incorporated in the reaction product in one ormore of a number of different ways. Thus, for example, the stabilizermay be added to the solutio nof rubber or other polyunsaturated highmolecular Weight reactant before the same is brought into reactiveengagement with the sulfur dioxide or other acidifying compoundemployed; alternatively, the stabilizer may be added to the mediumcontaining the acidifying com pound. The practice of either of theforegoing methods requires that the stabilizer be soluble, or at leastdispersible in, the liquid medium present, and preferably it should inno way interfere with the desired reaction between the respectiveunsaturated and acidic compounds. Since some such interference mayoccur, particularly as the concentration of stabilizer is increased orthe more alkaline stabilizers are employed, the preferred manner ofadding the stabilizer is to bring a solution thereof into contact withthe already formed reaction product, preferably when the latter is stillin the swollen condition due to its manner of production in thecoagulating bath and/or as a result of subsequent washing or soakingsteps. Thus, filaments produced by spinning a solution of peroxideactivated rubber into an ethanol-water-sulfur dioxide coagulating bathmay thereafter be immersed in a solution of a stabilizer, as potassiumthiocyanate in ethanol, for example, and left therein for any desiredperiod of time. Other appropriate solvents are acetone, propanol,butanol and methyl ethyl ketone. On being withdrawn from the stabilizersolution, the filaments may then be washed in the conventional manner,stretched, dyed or otherwise treated, following which they may be driedand used. If desired, one or more of such washing, drying, stretchingand/or dyeing steps may intervene between the actual precipitation ofthe filaments in the coagulating bath and their immersion in thestabilizer solution. Alternatively, the filaments may be treated in thedried (unswollen) condition with a solu--' tion of the desiredstabilizing compound, preferably in a solvent such as benzene, ethylalcohol, acetone or ethyl acetate which acts to swell the filament,though non-filament swelling solvents such as water may be employed inmany cases. The stabilizers may also be applied otherwise than byimpregnation. Thus, the material may be contacted with dispersions ofstabilizers or with an atmosphere which contains the stabilizers in thevaporous or atomized state. In the latter case a solution of thestabilizer may be atomized, if desired.

The concentration of stabilizer to employ, whether the same be added tothe unreacted materials, or is applied as a solution to the alreadyformed reaction product, is not critical. Thus, good results areobtained with solutions containing from about 0.1 to by weight of astabilizer, and some improvement can be effected even when using smallerquantities than 0.1%. Preferably, however, the concentration ofstabilizer should be at least 0.5% based on the entire weight of thesolution, with concentrations of more than 10% seldom being justified interms of improved results.

The period during which any given reaction product should be left in astabilizer solution will vary depending on a number of circumstances.Thus, in the case of filaments and other small shapes the soaking periodmay be somewhat shorter than with articles of greater cross section.Again, with more concentrated stabilizer solutions the soaking periodmay be somewhat shortened. Another factor is the ease with which thereaction product is able to take up the stabilizer solution, freshlyformed, undried products (i. e. swollen filaments) being considerablymore receptive to the stabilizer solution than dried ones. In general,immersion periods of from 1 to minutes are satisfactory with swollenfilaments though soaking periods of one or more hours are desirable whentreating dried filaments. In all cases extension of the soaking time isin no way harmful and in many cases proves of considerable benefit.Where the stabilizer is added to the unreacted solution of rubber orsulfur dioxide, for example, no modification need be made in the normalprocess by which said compounds are reacted.

Of more importance than the duration of the treatment with stabilizersolution is the temperature thereof. It forms a feature of the presentinvention that improved results are obtained by employing a heatedstabilizer solution, by which term is meant a solution having atemperature of C. or above, and preferably between 50 and 150 C. The useof such heated solutions serves in a measure to fix the stabilizer inthe reaction product, thereby increasing its resistance to removalparticularly following washing or other treating steps.

Still further improved results, notably as regards increased stabilityfollowing soap-washing and/or alkali-treating steps, are achieved bysubjecting reaction products already impregnated with stabilizercompound to a treatment involv-' ing heating said products in a gaseousenvironment such as air or nitrogen. The temperatures employed in thisheating step may range from about 50 to 250 0., though temperatures offrom about 80 to 150 C. are preferred. Effective treatments carried outin the latter temperature range 6. normally take from to 4 or morehours, the

relatively higher temperature permitting effective use of the shortertreating intervals. This so called dry heating step may be practicedwith beneficial results no matter whether the imgii pregnation treatmentreferred to in the preceding paragraph be conducted at elevatedtemperatures or not, though as a general rule the one heating treatmentre-enforces the other.

It has also been found that improved results 5-3 as regards fixation ofstabilizer may be obtained by utilizing stabilizer compounds such asallyl isocyanate and'allyl thiocyanate which contains one or morealkenyl or other unsaturated, aliphatic groups. Such unsaturatedstabilizing '53 compounds are preferably introduced into a solution ofrubber or other high molecular weight reactant prior to its reactionwith the acidic compound if the full effect of the stabilizationtreatment is to be obtained, for it seems a): quite probable that underthese circumstances the stabilizer enters into, and chemically forms apart of, the final reaction product.

The following example illustrates the present invention in various ofits embodiments:

& EXAMPLE The material to be stabilized was a reaction product of anatural rubber with sulfur dioxide in the form of dry filaments having asulfur content of 22% by weight, which material was produced by spinninga solution of natural rubber and tetralin hydroperoxide into a sulfurdioxidecontaining coagulating bath, and thereafter stretching, washingand drying the filaments in 45 air at room temperature. Samples of thesedried filaments were then soaked for four hours in solutions of variousstabilizers in ethanol as indicated in the following table, which alsoshows the concentration and temperature of each solution. Following thesoaking treatment the filaments were cursorily rinsed with ethanol andagain dried in air. Some of the samples were then washed for periods offour hours at C. in 5 a 0.4% solution of Marseilles soap. The stabilitywas ascertained by the quantity of S02 split off per unit of weight fromthe material to be examined when heated in a current of air for twohours at 125 C. These quantities are expressed 60 in percentages of thequantity of S02 split off per unit of weight in a blank test.

The invention claimed is:

1. The method of increasing the resistance to deterioration of a productformed on the reaction of natural rubber with sulfur dioxide, saidmethod comprising impregnating said productv with a solution containingfrom 0.1 to 20% ammonium thiocyanate.

2. The method of increasing the resistance to deterioration of a productformed on the reaction of natural rubber with sulfur dioxide, saidmethod comprising impregnating said product with a solution containingfrom 0.1 to 20% potassium thiocyanate.

3. The method of increasing the resistance to deterioration of a productformed on the reaction of natural rubber with sulfur dioxide, saidmethod comprising impregnating said product with a solution containingfrom 0.1 to 20% of an alkali metal thiocyanate.

4. The method of increasing the resistance to deterioration of a productformed on the reaction of natural rubber with sulfur dioxide, saidmethod comprising impregnating said product with a solution containing atotal of from 0.1 to 20% of at least one stabilizer compound selectedfrom the group consisting of the salts and esters of thiocyanic acid inwhich the alkyl group contains from 1 to carbon atoms.

5. The method of claim 4 wherein the said stabilizer compound isincorporated in said reaction product by immersing the product in aheated solution of the compound.

6. The method of claim 4 wherein there is added the step of heating thestabilizer-containing product in a gaseous environment.

7. The method of increasing the resistance to deterioration of a productformed on the reaction of sulfur dioxide with a rubbery polymer of atleast one compound selected from the group consisting of the conjugateddiolefins and chloroprene, said method comprising impregnating saidproduct with a solution containing from 0.1 to 20% of a stabilizercompound selected from the group consisting of the salts and esters ofthiocyanic acid in which the alkyl group contains from 1 to 5 carbonatoms.

8. In a method whereby a solution of natural rubber and tetralinhydroperoxide is injected into a coagulating bath containing availablesulfur dioxide, whereby there is precipitated in the bath a reactionproduct of the rubber and sulfur dioxide in the form of a continuous,swollen filament which is then withdrawn from the bath, the stepcomprising impregnating the still swollen filament with a solutioncontaining a total of from 0.1 to 20% of at least one stabilizercompound selected from the group consisting of the salts and esters ofthiocyanic acid in which the alkyl group contains from 1 to 5 carbonatoms.

9. The method of claim 8 wherein the stabilizer compound employed isammonium thiocyanate.

10. The method of claim 8 wherein the stabilizer compound employed is analkali metal thiocyanate.

11. In a method wherein a solution of a rubbery polymer of at least onecompound selected from the group consisting of the conjugated diolefinsand chloroprene is injected into a coagulating bath containing availablesulfur dioxide, whereby there is precipitated in the bath a reactionproduct of the rubbery polymer with sulfur dioxide in the form of acontinuous swollen filament; which is then withdrawn from the bath, thestep comprising impregnating the still swollen filament with a solutioncontaining a total of from 0.1 to 20% of at least one stabilizercompound selected from the group consisting of the salts and esters ofthiocyanic acid in which the alkyl group contains from 1 to 5 carbonatoms.

12. The method of increasing the resistance to deterioration of aproduct formed on the reaction of natural rubber with sulfur dioxide,said method comprising impregnating said product with a solutioncontaining at least 0.1% ammonium thiocyanate and at least 0.1%hexamethylenetetramine, the total amount of ammonium thiocyanate andhexamethylenetetramine in said solution being from 0.2 to 20% by Weight.

13. A novel composition of matter comprising a reaction product ofsulfur dioxide with a high molecular weight polymer of adiene-hydrocarbon, which reaction product is impregnated with astabilizer compound selected from the group consisting of alkali metalthiocyanates, ammonium thiocyanates and alkyl esters of thiocyanic acidin which the alkyl group contains from 1 to 5 carbon atoms, saidstabilizer compound being present in an amount sufficient to increasethe resistance of the reaction product against deterioration.

14. The composition of claim 13 wherein the polyunsaturated compound isnatural rubber and wherein the reaction product is impregnated withammonium thiocyanate.

15. The composition of claim 13 wherein the polyunsaturated compound isnatural rubber and wherein the reaction product is impregnated withalkali metal thiocyanate.

J OHAN MICHAEL GOPPEL.

GOTTFRIED ERNST RUIVISCHEIDT.

JOHANNES THOMAS HACKMANN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS De Nie et al. May 10, 1949

1. THE METHOD OF INCREASING THE RESISTANCE TO DETERIORATION OF A PRODUCTFORMED ON THE REACTION OF NATURAL RUBBER WITH SULFUR DIOXIDE, SAIDMETHOD COMPRISING IMPREGNATING SAID PRODUCT WITH A SOLUTION CONTAININGFROM 0.1 TO 20% AMMONIUM THIOCYANATE.